He was challenged by the teenager and Sowerbutts said he wanted the drink he had brought with him.

The youth asked him to leave but Sowerbutts pushed him in the living room. He told him not to be cheeky, forced him on a settee and pointed a knife blade on the lad’s left cheek.

Fiona Cortese, prosecuting, said: “The victim tried to push him off. But the defendant slashed him across the cheek with the knife.”

Sowerbutts left the flat in Ashfield Court, Cross Heath, and threw the knife down a grid. The victim went to hospital and had an operation where he received 26 stitches.

The court heard the teenager has lost confidence and has become paranoid and jumpy following the incident.

Sowerbutts was arrested hours after the slashing on July 7. He told police he became angry. He added he had drunk vodka which made him violent. He could not remember going in the flat twice, pinning his victim to the sofa or recall having or using a knife. He attributed his memory loss to drinking too much booze.

The court heard he has a conviction for wounding in 2007 when he kicked and stamped on a man’s face.

And he was jailed for 20 months last year for possessing an offensive weapon and grievous bodily harm, when he slashed a friend with a knife causing serious injuries to his hand as he protected his face. He was released from prison on licence on May 24 – about six weeks before the latest offence.

Nick Tatlow, mitigating, said there was no evidence that Sowerbutts took the knife to the scene.

Mr Tatlow conceded the injury was ‘horrific’. But he said it was caused by a single slash and there was no follow-up to inflict further injury.

Mr Tatlow added: “He acknowledges he did something very wicked and very wrong with very unpleasant and lasting injuries for his victim.”

Judge Paul Glenn said Sowerbutts met the criteria of a dangerous offender but he believes the extended sentence will provide the public with sufficient protection.

“Your victim was 17,” said the judge. “You and another man went to his flat. You had never previously met him. There was an argument. He asked you to leave as he was entitled to do. You attacked him with a large knife. You slashed it across his cheek.”

Judge Glenn added: “Pictures of that injury are sickening. That young man was left with permanent scarring.”